My dear Friend,— As you express a wish to know my recent impressions respecting the great telescope, I can say that they are very satisfactory. When I saw it six weeks ago the first of the two great specula was just polished; and though the essential parts of the equatoreal were in position, and one could estimate the facility with which it could be managed, the optical part of the telescope remained incomplete. Now, I found the great and small specula in their places, a finder of four inches aperture attached, the circles divided, and the clock for driving the telescope enshrined in the pier. One thing was wanting, weather fit for trying its power; and during eighteen nights there was only one of even middling goodness. That, however, was sufficient to prove that the instrument is thoroughly up to its intended work. I examined several nebulae and clusters, with whose appearance in Lord Rosse’s six-feet reflector I am familial, and the difference was far less than I expected. I may specify among them 51 Messier, whose spirals were seen on strong aurora, and the nebula in Aquarius, with its appendages like the ring of Saturn. Its definition of stars is very good: a Lyræ had as small and sharp an image as I ever saw on such a night; and a few pretty close double stars were well and clearly separated. Part of this is probably due to the lattice-tube, which permits the escape of heated air, but more to the figure of the speculum, which is truly parabolic. The peculiar nature of the mounting brings the circles completely within reach of the observer s assistant; and the mechanical appliances for the motions in right ascension and polar distance are so perfect, that we set the instrument on the faint objects winch; we were examining with great facility and rapidity. One man can reverse the telescope in a minute and a quarter; the quick motion in polar distance is of course far easier, and the slow one acts more like the tangent screw of a circle than the mover of such a huge mass. The clock is rather gigantic, but does its work with great precision, the objects which I examined remaining steady on the wire as long as I watched them; and there is at ingenious and new contrivance for suiting its speed to planets or the moon, There remain but a few matters to be completed; the second great speculum is nearly polished, the glass small one is ready; the micrometer and observing-chair are not commenced, nor the photographic apparatus and spectroscope. These two last are no part of Mr. Grubb’s contract; but the Committee thought themselves justified by the correspondence in ordering them, as their cost is small, and they will add greatly to the utility oi the telescope. In. the fine sky of Melbourne it will, I trust, yield spectroscopic results surpassing any that have as vet been obtained. That it will realize fully the expectations of the people whose enlightened liberality has ordered its construction I am quite certain; but I am not so certain that it will retain its present perfection very long if exposed without some shelter. It is true that Mr. Cooper’s great achromatic has stood exposed to the rain and wind of Connaught for more than thirty years, and is still serviceable; but besides its inferior size it is of coarser workmanship, and is provided with fewer of those beautiful contrivances which in this instrument make its movements so easy. At Melbourne the rain of Markree is not to be feared; but if one may judge from its position on the verge of a great continent, and from the analogy of India and the Cape, another enemy is to he dreaded, the fine dust which winds from the interior will probably bring. This would find its way into all the bearings, and besides logging their action would grind them out of truth. The danger of this induces me, after careful discussion with Messrs. Le Sueur and the two Grubbs, n lay before you my views, which (if you think them sound) you may hold it advisable to mention to the authorities of Victoria. Three modes occur to me of covering the telescope. In any case it must be surrounded by a wall, for the comfort of the observer and to prevent in trusion. This wall may support a moveable covering of such a kind as let the instrument be pointed to every part of the sky.
On the Systematic Errors of the Moon in Right Ascension
